1. Field of the Invention
The present invention relates to an optical waveguide device and to a method of manufacturing this device.
2. Description of the Background Art
Japanese Patent Application Publication No. 2000-121859 discloses a method of manufacturing an embedded type optical waveguide device. This method involves manufacturing an optical waveguide device by (1) depositing an undercladding layer over a silica glass substrate, (2) forming a mask over the undercladding layer, (3) using this mask to form a groove for accommodating a core, (4) depositing a core layer over the undercladding layer, (5) forming a core by leaving the core layer inside the groove and removing other portion of the core layer on the undercladding layer by chemical-mechanical polishing, and (6) forming an overcladding layer over the core and the undercladding layer.
Japanese Patent Application Publication No. 2003-161852 discloses a method of manufacturing a dielectric waveguide device. This method involves manufacturing an optical waveguide device by (1′, 2′) forming a mask over a glass substrate having a refractive index of 1.445, (3′) forming a groove in the substrate by using RIE to etch the portion of the substrate exposed from the mask, (4′) forming a glass film with a refractive index of 1.456 that will serve as a core, using an ICP-CVD apparatus, in the groove and over the mask, (5′) removing the mask by wet etching, and (6′) depositing a glass layer that will serve as overcladding.
With these methods, after a groove for accommodating a core has been formed on an undercladding layer, the core is formed in the groove. In order to make the refractive index of the core greater than the refractive index of the cladding, the core is doped with a dopant that increases the refractive index. More specifically, a gas for adding germanium is added to the raw material gas when the core film is formed. As a result, the core glass has a composition of SiOX—GeOY. The core film is gradually deposited on the sides and bottom of the groove. Researches conducted by the inventors revealed that the germanium concentration in the two side walls of the core film inside the groove is higher than that in the middle part of the core, meaning that the germanium dopant is not evenly distributed. An inconsistent germanium concentration leads to an imbalance in the refractive index profile.